1. Technical Field of the Invention
The present invention relates generally to a fuel injection system which may be employed with automotive internal combustion engines to learn the quantity of fuel actually sprayed by a fuel injector for correcting an on duration or injection duration for which the fuel injector is to be opened to spray the fuel desirably, and more particularly to such a fuel injection system designed to learn an average of injection quantities for correcting the injection duration.
2. Background Art
There are known fuel injection systems for automotive internal combustion engines which are designed to instruct a fuel injector spray a target quantity of fuel to learn the quantity of fuel actually sprayed (will also be referred to as an actual injection quantity below) and correct an injection duration based on a deviation of the actual injection quantity from the target quantity. For example, Japanese Patent First Publication No 2005-155360 proposes such an injection quantity learning system. This system works to execute an injection quantity learning operation when the engine is decelerating and no fuel is being sprayed into the engine and calculate the actual injection quantity based on a change in speed of the engine arising from the spraying of fuel thereinto. The system instructs the fuel injector to spray the fuel in a cycle and determines an average of sequentially calculated actual injection quantities for use in comparison with the target quantity.
A change in speed of the engine proceeding from, for example, undulations of the road surface will result in an undesirable variation in the actual injection quantity, as calculated. This leads to the instability of accuracy in calculating the average of the actual injection quantities for use in the comparison with the target quantity.